SERCA1 Overexpression in Skeletal Muscle Attenuates Muscle Atrophy and Improves Motor Function in a Mouse Model of ALS.

Background: Amyotrophic lateral sclerosis (ALS) is characterized by progressive loss of muscle mass and muscle function. Previous work from our lab demonstrated that skeletal muscles from a mouse model of ALS show elevated intracellular calcium (Ca2+) levels and heightened endoplasmic reticulum (ER) stress.

Objective: To investigate whether overexpression of sarcoplasmic reticulum (SR) Ca2+ ATPase 1 (SERCA1) in skeletal muscle would improve intracellular Ca2+ handling, attenuate ER stress, and improve motor function ALS transgenic mice.

Single-cell transcriptomic analysis of the identity and function of fibro/adipogenic progenitors in healthy and dystrophic muscle.

Fibro/adipogenic progenitors (FAPs) are skeletal muscle stromal cells that support regeneration of injured myofibers and their maintenance in healthy muscles. FAPs are related to mesenchymal stem cells (MSCs/MeSCs) found in other adult tissues, but there is poor understanding of the extent of similarity between these cells. Using single-cell RNA sequencing (scRNA-seq) datasets from multiple mouse tissues, we have performed comparative transcriptomic analysis.

Altered muscle niche contributes to myogenic deficit in the D2-mdx model of severe DMD.

Lack of dystrophin expression is the underlying genetic basis for Duchenne muscular dystrophy (DMD). However, disease severity varies between patients, based on specific genetic modifiers. D2-mdx is a model for severe DMD that exhibits exacerbated muscle degeneration and failure to regenerate even in the juvenile stage of the disease.

Altered muscle niche contributes to myogenic deficit in the D2- model of severe DMD.

Lack of dystrophin is the genetic basis for the Duchenne muscular dystrophy (DMD). However, disease severity varies between patients, based on specific genetic modifiers. D2- is a model for severe DMD that exhibits exacerbated muscle degeneration and failure to regenerate even in the juvenile stage of the disease.

Absence of the Z-disc protein α-actinin-3 impairs the mechanical stability of Actn3KO mouse fast-twitch muscle fibres without altering their contractile properties or twitch kinetics.

Background: A common polymorphism (R577X) in the ACTN3 gene results in the complete absence of the Z-disc protein α-actinin-3 from fast-twitch muscle fibres in ~ 16% of the world's population. This single gene polymorphism has been subject to strong positive selection pressure during recent human evolution. Previously, using an Actn3KO mouse model, we have shown in fast-twitch muscles, eccentric contractions at L + 20% stretch did not cause eccentric damage.

Pathogenic role and therapeutic potential of fibro-adipogenic progenitors in muscle disease.

Aside from myofibers, numerous mononucleated cells reside in the skeletal muscle. These include the mesenchymal cells called fibro-adipogenic progenitors (FAPs), that support muscle development and regeneration in adult muscles. Recent evidence shows that defects in FAP function contributes to chronic muscle diseases and targeting FAPs offers avenues for treating these diseases.

Interrogation of Dystrophin and Dystroglycan Complex Protein Turnover After Exon Skipping Therapy.

Recently, the Food and Drug Administration granted accelerated approvals for four exon skipping therapies -Eteplirsen, Golodirsen, Viltolarsen, and Casimersen -for Duchenne Muscular Dystrophy (DMD). However, these treatments have only demonstrated variable and largely sub-therapeutic levels of restored dystrophin protein in DMD patients, limiting their clinical impact. To better understand variable protein expression and the behavior of truncated dystrophin protein in vivo, we assessed turnover dynamics of restored dystrophin and dystrophin glycoprotein complex (DGC) proteins in mdx mice after exon skipping therapy, compared to those dynamics in wild type mice, using a targeted, highly-reproducible and sensitive, in vivo stable isotope labeling mass spectrometry approach in multiple muscle tissues.

Human muscle stem cells are refractory to aging.

Age-related loss of muscle mass and strength is widely attributed to limitation in the capacity of muscle resident satellite cells to perform their myogenic function. This idea contains two notions that have not been comprehensively evaluated by experiment. First, it entails the idea that we damage and lose substantial amounts of muscle in the course of our normal daily activities.

Coping with the calcium overload caused by cell injury: ER to the rescue.

Cells maintain their cytosolic calcium (Ca) in nanomolar range and use controlled increase in Ca for intracellular signaling. With the extracellular Ca in the millimolar range, there is a steep Ca gradient across the plasma membrane (PM). Thus, injury that damages PM, leads to a cytosolic Ca overload, which helps activate PM repair (PMR) response.

Endoplasmic reticulum maintains ion homeostasis required for plasma membrane repair.

Of the many crucial functions of the ER, homeostasis of physiological calcium increase is critical for signaling. Plasma membrane (PM) injury causes a pathological calcium influx. Here, we show that the ER helps clear this surge in cytoplasmic calcium through an ER-resident calcium pump, SERCA, and a calcium-activated ion channel, Anoctamin 5 (ANO5).

TGF-β-driven muscle degeneration and failed regeneration underlie disease onset in a DMD mouse model.

Duchenne muscular dystrophy (DMD) is a chronic muscle disease characterized by poor myogenesis and replacement of muscle by extracellular matrix. Despite the shared genetic basis, severity of these deficits varies among patients. One source of these variations is the genetic modifier that leads to increased TGF-β activity.

Dysregulation of Mitochondrial Ca Uptake and Sarcolemma Repair Underlie Muscle Weakness and Wasting in Patients and Mice Lacking MICU1.

Muscle function is regulated by Ca, which mediates excitation-contraction coupling, energy metabolism, adaptation to exercise, and sarcolemmal repair. Several of these actions rely on Ca delivery to the mitochondrial matrix via the mitochondrial Ca uniporter, the pore of which is formed by mitochondrial calcium uniporter (MCU). MCU's gatekeeping and cooperative activation are controlled by MICU1.

Morpholino-induced exon skipping stimulates cell-mediated and humoral responses to dystrophin in mdx mice.

Exon skipping is a promising genetic therapeutic strategy for restoring dystrophin expression in the treatment of Duchenne muscular dystrophy (DMD). The potential for newly synthesized dystrophin to trigger an immune response in DMD patients, however, is not well established. We have evaluated the effect of chronic phosphorodiamidate morpholino oligomer (PMO) treatment on skeletal muscle pathology and asked whether sustained dystrophin expression elicits a dystrophin-specific autoimmune response.

STAT3 in Skeletal Muscle Function and Disorders.

Signal transducer and activator of transcription 3 (STAT3) signaling plays critical roles in regulating skeletal muscle mass, repair, and diseases. In this review, we discuss the upstream activators of STAT3 in skeletal muscles, with a focus on interleukin 6 (IL6) and transforming growth factor beta 1 (TGF-β1). We will also discuss the double-edged effect of STAT3 activation in the muscles, including the role of STAT3 signaling in muscle hypertrophy induced by exercise training or muscle wasting in cachectic diseases and muscular dystrophies.

Calcium dysregulation, functional calpainopathy, and endoplasmic reticulum stress in sporadic inclusion body myositis.

Sporadic inclusion body myositis (IBM) is the most common primary myopathy in the elderly, but its pathoetiology is still unclear. Perturbed myocellular calcium (Ca) homeostasis can exacerbate many of the factors proposed to mediate muscle degeneration in IBM, such as mitochondrial dysfunction, protein aggregation, and endoplasmic reticulum stress. Ca dysregulation may plausibly be initiated in IBM by immune-mediated membrane damage and/or abnormally accumulating proteins, but no studies to date have investigated Ca regulation in IBM patients.

NAD+ repletion improves muscle function in muscular dystrophy and counters global PARylation.

Neuromuscular diseases are often caused by inherited mutations that lead to progressive skeletal muscle weakness and degeneration. In diverse populations of normal healthy mice, we observed correlations between the abundance of mRNA transcripts related to mitochondrial biogenesis, the dystrophin-sarcoglycan complex, and nicotinamide adenine dinucleotide (NAD) synthesis, consistent with a potential role for the essential cofactor NAD in protecting muscle from metabolic and structural degeneration. Furthermore, the skeletal muscle transcriptomes of patients with Duchene's muscular dystrophy (DMD) and other muscle diseases were enriched for various poly[adenosine 5'-diphosphate (ADP)-ribose] polymerases (PARPs) and for nicotinamide N-methyltransferase (NNMT), enzymes that are major consumers of NAD and are involved in pleiotropic events, including inflammation.

The SH3 and cysteine-rich domain 3 (Stac3) gene is important to growth, fiber composition, and calcium release from the sarcoplasmic reticulum in postnatal skeletal muscle.

Background: The SH3 and cysteine-rich domain 3 (Stac3) gene is specifically expressed in the skeletal muscle. Stac3 knockout mice die perinatally. In this study, we determined the potential role of Stac3 in postnatal skeletal muscle growth, fiber composition, and contraction by generating conditional Stac3 knockout mice.

SERCA1 overexpression minimizes skeletal muscle damage in dystrophic mouse models.

Duchenne muscular dystrophy (DMD) is characterized by progressive muscle wasting secondary to repeated muscle damage and inadequate repair. Elevations in intracellular free Ca²⁺ have been implicated in disease progression, and sarcoplasmic/endoplasmic reticulum Ca²⁺-ATPase 1 (SERCA1) overexpression has been shown to ameliorate the dystrophic phenotype in mdx mice. The purpose of this study was to assess the effects of SERCA1 overexpression in the more severe mdx/Utr(-/-) mouse model of DMD.

The role of proteases in excitation-contraction coupling failure in muscular dystrophy.

Duchenne muscular dystrophy (DMD) is one of the most frequent types of muscular dystrophy. Alterations in intracellular calcium (Ca(2+)) handling are thought to contribute to the disease severity in DMD, possibly due to the activation of Ca(2+)-activated proteases. The purpose of this study was twofold: 1) to determine whether prolonged excitation-contraction (E-C) coupling disruption following repeated contractions is greater in animals lacking both dystrophin and utrophin (mdx/Utr(-/-)) compared with mice lacking only dystrophin (mdx); and 2) to assess whether protease inhibition can prevent E-C coupling failure following repeated tetani in these dystrophic mouse models.

Perturbations in intracellular Ca2+ handling in skeletal muscle in the G93A*SOD1 mouse model of amyotrophic lateral sclerosis.

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease characterized by skeletal muscle atrophy and weakness, ultimately leading to respiratory failure. The purpose of this study was to assess changes in skeletal muscle excitation-contraction (E-C) coupling and intracellular Ca(2+) handling during disease progression in the G93A*SOD1 ALS transgenic (ALS Tg) mouse model. To assess E-C coupling, single muscle fibers were electrically stimulated (10-150 Hz), and intracellular free Ca(2+) concentration was assessed using fura-2.